Modifications of the infrared spectra from chemisorbed CO as a measure of hydrogen coverage of a nickel surface: Dependence of the spectra of chemisorbed ethylene on hydrogen coverage

Abstract The infrared absorption in the 2100-2000 cm −1 region from CO chemisorbed on silica-supported nickel is shown to be sensitive to the presence or otherwise of hydrogen co-adsorbed on the metal surface. A “hydrogen-covered” surface gives a v CO band near 2070 cm −1 ; a “bare” or “hydrogen-free” surface gives a band near 2040 cm −1 . Using this criterion it is shown that a “hydrogen-covered” surface prepared at 25 °C loses much of its hydrogen by pumping at 50 °C. Different spectra have been obtained (as previously by Eischens and Pliskin in 1958) from ethylene adsorbed on hydrogen-covered and bare nickel. The former spectra are stronger and show a particularly dominant band near 2890 cm −1 which is selectively removed by CO adsorption and also by hydrogenation. Closely similar spectra are obtained after hydrogenation of ethylene adsorbed on hydrogen-covered or bare nickel. It is concluded that intervening reports of similar spectra from ethylene initially adsorbed on nickel surfaces prepared so as to be hydrogen-covered or bare may result, in part, from heating effects in the infrared beam which under certain experimental conditions can remove some of the hydrogen from the surfaces prepared as hydrogen-covered.